Permanent magnetic focusing device for multi-cavity klystrons

ABSTRACT

A permanent magnetic focusing device for periodically guiding the electron beams of multicavity klystrons comprising axially arranged magnets that are radially magnetized in the same sense.

United States Patent Dubravec [4 1 May 23, 1972 [54] PERMANENT MAGNETIC FQCUSING 2,867,744 1/1959 Kompfner ..31s/3.s DEVICE FOR MULTLCA TY 2,944,182 7/1960 Rigrod ....3l5/3.5 VI 0| .3 I 3,375,400 3/1968 Schrumpf 315/35 [72] Inventor: Vladimir Dubravec, Kastanienallee, Ger- 3,366,904 1/1968 Schmidt ..315/5.35 X

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Primary Examiner-Herman Karl Saalbach [73] Assignee. Philips Corporation, New York, NY. Assistant Examiner s field Chamon' Jr [22] Filed: July 1, 1970 Attorney-Frank R. Trifari [21] App1.No.: 51,506 [57] ABSTRACT A permanent magnetic focusing device for periodically guid- Eifi E3852:31111111111111: $7951.?ii iiiflifi insweelemnbmofmumcamycomprising 581 Field of Search ..315/3.5,5.34,5.35;335/210 manged radially magnetized the same sense. [56] Merenc 6 Clains, 14 Drawing fi ures UNITED STATES PATENTS PATENTED MAY 23 I972 sum 1 0F 4 Fig.1B

1000- itB [e] INVENTOR.

by VLADIMIR DUBRAVEC AGENT PATENTEUMAY 23 m2 3 665 242 sum 2 OF 4 i---- L=P=l F g, 3A 1000 B(z)[G] INVENTOR.

Y VLADIMIR DUBRAVEC AGENT PATENTEDMM 23 I972 SHEET 3 UF 4 BY VLADIMIR DU BRAVE C AGENT PATENTEDMAY 2 3 m2 sum u [1F 4 Fig.7B

INVENTOR.

BY VLADIMIR DUBBAVE c- AGENT PERMANENT MAGNETIC FOCUSING DEVICE FOR MULTI-CAVITY XLYSTRONS The invention relates to a permanent magnetic focusing device for guiding long electron beams in multicavity klystrons by means of spatially periodic or quasi-periodic magnetic fields.

Periodic magnetic arrangements for klystrons are known from German Pat. specification 1,158,183. The permanent magnets are magnetized axially and arranged between the cavities. The magnetic flux is guided to the axis of the system by soft-iron yokes. A large loss occurs. Moreover, the arrangement has s comparatively large weight. For travelling wave guides periodic magnet arrangements are known which comprise magnet rings or magnet spoked wheels which are magnetized in the radial direction and are arranged one behind the other in the axial direction. The arrangements described in German Pat. application T 11091 and the US. Pat. No. 3,020,440 and the United Kingdom Pat. Specification No. 729,002, respectively, however, are not suitable for klystrons because no space is available for the resonators between the magnet elements.

It is the object of the invention to provide a focusing device for klystrons which has special advantages.

In a permanent magnetic focusing device for guiding long electron beams in multi-cavity klystrons by means of spatially periodic or quasi-periodic magnetic fields, according to the invention the magnetic fields are produced by magnet rings or magnet spoked wheels magnetized in the radial direction and arranged one behind the other in the axial direction, the magnet rings being united to form groups in which the individual rings and wheels, respectively, show intermediate spaces, each group comprising only elements which are magnetized in the same sense, the groups being arranged between the resonators around the drift tube. The individual groups may all be magnetized in the same sense or be magnetized alternately in the opposite sense. Moreover, according to the invention, the magnet rings and magnet spoked wheels, respectively, may be arranged on the inner and/or outer surfaces of soft-magnetic pole shoes serving for adjusting the field distribution and for producing the rotational symmetry and which also project in the resonant cavity between the magnet groups and may be constructed as parts of the drift tube.

In addition, according to the invention, the magnet rings and magnet spoked wheels, respectively, may be arranged so as to comprise an intermediate space which serves for adjusting the field distribution and, if desirable, for cooling the drift tube, which intermediate space is free from ferromagnetic materials.

Furthermore, the arrangements according to the invention may also be constructed so that the Fourier component of the B (z distribution with the period 1. in periodic arrangement of individual magnet ring groups at the distance 1 from one another, is approximately or exactly suppressed.

In order that the invention may be readily carried into effect, it will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which I FIGS. la and 1b diagrammatically shows a focusing arrangement for a multi-cavity klystron in entirety and in part, respectively.

FIG. 2 shows field distributions B (z) of, for example, 1 and 2 magnet rings, respectively.

FIGS. 3a, 3b, 4a and 4b show focusing arrangements and graphs illustrating the axial induction distributions B (z) for periodic and quasi-periodic arrangements, respectively, of

permanent magnet ring groups of the same (FIGS. 3a and 3b) and alternate (FIGS. 40 and 4b) polarity.

FIGS. 5a and 5b shows an arrangement of a permanent magnetic focusing system with full suppression of the first Fourier component of the distribution E (2).

FIGS. 6:; and 6b shows an arrangement of a permanent magnetic focusing system for exemplifying several magnet rings per group and suppressed first Fourier component B (z).

FIGS. 7a and 7b shows a permanent magnetic focusing arrangement and distribution graphs according to the invention for a special embodiment.

FIG. 8 shows a construction of a magnet element in the form of a spoked wheel.

The system in FIGS. 1a and 1b consists of oxide ceramic magnet rings 1 surrounding the drift tube, which rings are arranged in the narrow spaces between the resonant cavities 2. Reference numeral 4 denotes the diagrammatically shown electron gun system and reference numeral 5 denotes the diagrammatically shown collector of the klystron. The diagrammatically shown sections 6 of the drift tube are each time arranged in known manner between the resonant cavities 2. The soft-iron pole shoes 3 engage the magnet rings on the inside and outside.

For reasons of geometry, only magnetic field periods L which are very long compared with travelling wave tubes are considered in klystrons. If the ratio magnet height h to resonator height h is comparatively small, the use of magnet rings magnetized in the axial direction results in too low ratios of the axial induction in the resonator B to the induction B on the axis of the magnet section and consequently in a beam diameter ripple which is much too high. In these circumstances the radial magnetization of magnet rings provides better results in a new focusing design which is adapted to the given field-producing possibilities. As an example of such a focusing design, a UHF high-power klystron will be described.

The axial induction distribution B (z) of a thin, radially magnetized magnet ring can be represented approximately by the equation where R, inside radius and R outside radius of the magnet ring, 2 1 magnet ring height, z distance of the point of observation situated on the ring axis from the ring center and I magnetic polarization in the magnetic material (in ferrites I B From this it may be seen that a magnet ring can be proportionally increased or decreased without the relative field distribution z B )/l varying.

After using the superposition principle, which holds good very exactly at least in ferrites, this equation permits the calculation of the field distribution B (z) of a system of magnet rings without soft-magnetic.flux-converting means by simple addition of the individual ring fields.

The field distributions B (z) of, for example, one and of two magnet rings, respectively, of dimensions R,,/R,/2 I 134/5 7/14 mm are shown in FIG. 2. The curves I each give the field of an individual ring and the curve II the resulting field in G (Gauss). By periodic and quasi-periodic arrangement, respectively of such multi-ring groups of the same or alternate polarities, periodic and quasi-periodic axial induction distributions 8 (z), respectively, are obtained by the superposition. The focusing properties of these arrangements can be derived by way of example from FIGS. 3a, 3b, 4a and 4b.

Since the period L and the Fourier components of the induction distribution B(z) are not decisive of the periodic focusing but the period P of the function 'B (Z =B 9/3 (B =(effective induction? and its Fourier coefficient A (n O, l, 2 it must be tried to keep the first Fourier component of the distribution 8' (z) with the period P L as small as possible or make it disappear because the first Fourier component of B (z) has the greatest beam diameter ripple.

As may be seen from FIGS. 3a and 3b in which and example of a periodic arrangement according to the invention is shown of the magnet ring groups magnetized in the same sense, the comparatively large first Fourier component (period P, L) of the distribution 8 (z) can be partly or fully suppressed a. by the distance variation between the individual magnet rings of a group,

b. by providing suitably shaped pole shoes as shown in FIG.

3 which intensify the magnetic field between the groups and vary the increase in the field within a group as is desired,

c. by using magnet rings of a larger diameter d. by varying the number of rings in a group from one onwards, and

e. by varying the distance between the groups, i.e. the

period L.

FIGS. a and 5b shows by way of example a full suppression of the first Fourier component of the distribution B (z) reached by using the measures indicated in (a) and (e). The additional use of the remaining measures (a) to (e) would have permitted a suppression of the fundamental frequency also with larger period lengths L and the same ring diameter. According to the invention the arrangement is therefore constructed so as to enable a suppression of the first Fourier component as well as a large flexibility in realizing the desirable field distributions with large periods L. The field strength can also be adjusted inter alia by the magnetic shunting of the individual rings without essentially varying the distribution 19 (z)- The broken-line curves III give the field of a pair of rings and the solid-line curves the combination field IV for d 2 cm and V for d= 3 cm.

FIGS. 4a and 4b shows a periodic arrangement of magnet ring groups of alternate polarities. In case of large period lengths L a suppression of the first Fourier component of the distribution B" (z) can be achieved only partly with the measures indicated in a) to e), while with small period lengths it cannot be achieved at all. A longand short period L, respectively, is to be understood to mean only the value of the distance L between the groups as compared with the diameter of the magnet ring and not the absolute value L. The shortperiod version of a periodic arrangement of magnet ring groups polarized in the same sense would actually serve no purpose since the fields of adjacent groups would be appreciably neutralized, while the arrangement of groups polarized in the opposite sense is of importance both for the short-period and for the long-period version. VI denotes the ring fields, VII a field of a pair of rings and VIII the combination field.

FIG. 5a diagrammatically shows three drift tube sections 6 having magnet rings 1 magnetized in the same sense. If desirable, the pole shoes 3 may penetrate the drift tubes for a stronger influencing of the increase in the field or the field strength as is shown in broken lines in the upper part of FIG. 5b. IX denotes the field of a pair of rings and X the combination field.

FIGS. 60 and 6b shows an embodiment having several magnet rings per group and characteristics illustrating suppressed first Fourier components of E (z). For producing the rotational symmetry all the individual rings comprise on their inner and outer conical surface soft magnetic pole shoe rings which can be provided on individual rings instead of on the whole group collectively so as to avoid the shunting effect. XI shows a field of a pair of rings, XII the field of the groups of four rings and XIII the combination field. In the quasi-periodic arrangements these constructions hold good approximately although in circumstances special field distributions may be desirable which, however, are realized in the same manner.

For suppressing said Fourier component with a period length L 2 l which is as large as possible, the individual magnet rings are replaced according to the invention each time by a group of thin rings or disks magnetized radially in the same sense and the distribution of which is then chosen to be so that the increase in the field within the group assumes a form which is desirable for optimizin the beam diameter variation (adapting the declining field o the wave front to the part of the B(z) curve to the increasing part, for example). Furthermore, according to the invention, the E (z) maxima are shifted as far as possible from the group center by providing suitable soft-magnetic pole shoes on the drift tubes and hence the field distribution is additionally influenced as is desirable and furthermore, according to the invention, the distance 1 between the centers of the adjacent groups magnetized in the opposite sense and the diameter of the magnet rings, respectively, is chosen to be so that the first Fourier component of the resulting B (z) distribution (period P 1) becomes minimum, i.e. that the E (z) maxima are approximately evenly distributed along the axis.

Such a periodic arrangement according to the invention is shown in FIGS. 7a and 7b. Since in the quasi-periodic case the distances 1 between the magnet groups can considerably deviate from each other, the groups must be designed individually if good guidance is desirable. The above-described measures place available, for this case also, a rather large number of free parameters for adjusting desirable field distribution so that a good matching to the individual requirements is ensured. The B(z) curve is shown in solid lines and the 8 (2) curve is shown in broken lines.

The individual magnet rings can in all cases be constructed by a spoke-shaped arrangement of permanent magnetic rods 11 shown in FIG. 8, in which the fine structure of the field adjacent the axis can be suppressed, for example, by an annular pole shoe 13. When the permanent magnets are arranged around the drift tube of a finished klystron, they must be constructed in two or several parts.

What is claimed is:

1. An electron discharge tube of klystron type comprising an evacuated housing forming a plurality of drift tubes and cavity resonators interposed between the drift tubes, an electron gun within said housing for producing an electron beam, a collector within said housing distally spaced from said electron gun for receiving said electron beam, and a plurality of groups of axially aligned permanent magnetic focusing devices having intermediate spaces between said groups and surrounding said drift tubes for forming magnetic field distributions to periodically guide said electron beams through said drift tubes and said resonators, said resonators being arranged within said intermediate spaces, said magnets in each group being radially magnetized in the same sense.

2. An electron discharge tube as claimed in claim 1 wherein said magnets are toroidally shaped.

3. An electron discharge tube as claimed in claim 1 wherein said magnets are shaped in the form of wheel spokes.

4. An electron discharge tube as claimed in claim 1 further comprising soft-magnetic pole shoes arranged on said magnets for adjusting magnetic field distribution and producing rotational symmetry of said electron beam, said pole shoes projecting into the cavity resonators from said drift tubes.

5. An electron discharge tube as claimed in claim 1 wherein said intermediate spaces are free from ferromagnetic materials, provide a capability for adjusting the magnetic field distribution and provide for cooling the drift tubes.

6. An electron discharge tube as claimed in claim 1 wherein said magnetic field has a flux distribution described by a 13 (z) component of a Fourier Series with the period 1 in periodic arrangement of individual magnet groups a distances 1 from each other, said magnets being arranged at distances I from each other for substantially suppressing the dependence of said distribution upon a first Fourier component thereby reducing beam diameter ripple.

"UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECHON Y PatentNo. 3,665,242 7 Dated Maw 23 1972 Inventor(s) Vladimir Dubravec It is certified that error appears in the above-identified patent and that sid LettersPatent are hereby corrected as shown below:

On the cover sheet, insert the following: [30] Foreign Priority Data Germany July 2, 1969 P l933586.5

Signed and sealed this 8th day of May 1973.

(S AL) Attest:v

' EDWARD M. FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Coxmnissioner of Patents USCOMM-DC 6O376-P 69 u.s GOVERNMENT PRlNTING OFFICE: 1969 o-3e6-3:4.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,665,242 D t Mav 23 197:

Inventor(s) Vladimir Duhralvec 4 It is certified that'error appears in the above-idehtified patent and that said Letters Patent are hereby corrected as shown below:

v 0n the cover sheet, insert the following: [[30] 1 Foreign Priority Data Germany 7 July 2, 1969 P 'l933586,5 I

Signed and sealed this Sth'day of May 1973.

(S Attest:

EDW ARD'M.FLETCHER,JR. 3 ROBERT GOTTSCHALK Attestingnfficer v Commissioner of Patents =or=w .=:--25-: @049 v US-COMNI-DC 60516.5

U.S. GOVERNMENT PRINTING OFFICE: I969 0 36 6-334, 

1. An electron discharge tube of klystron type comprising an evacuated housing forming a plurality of drift tubes and cavity resonators interposed between the drift tubes, an electron gun within said housing for producing an electron beam, a collector within said housing distally spaced from said electron gun for receiving said electron beam, and a plurality of groups of axially aligned permanent magnetic focusing devices having intermediate spaces between said groups and surrounding said drift tubes for forming magnetic field distributions to periodically guide said electron beams through said drift tubes and said resonators, said resonators being arranged within said intermediate spaces, said magnets in each group being radially magnetizEd in the same sense.
 2. An electron discharge tube as claimed in claim 1 wherein said magnets are toroidally shaped.
 3. An electron discharge tube as claimed in claim 1 wherein said magnets are shaped in the form of wheel spokes.
 4. An electron discharge tube as claimed in claim 1 further comprising soft-magnetic pole shoes arranged on said magnets for adjusting magnetic field distribution and producing rotational symmetry of said electron beam, said pole shoes projecting into the cavity resonators from said drift tubes.
 5. An electron discharge tube as claimed in claim 1 wherein said intermediate spaces are free from ferromagnetic materials, provide a capability for adjusting the magnetic field distribution and provide for cooling the drift tubes.
 6. An electron discharge tube as claimed in claim 1 wherein said magnetic field has a flux distribution described by a B2 (z) component of a Fourier Series with the period 1 in periodic arrangement of individual magnet groups a distances 1 from each other, said magnets being arranged at distances 1 from each other for substantially suppressing the dependence of said distribution upon a first Fourier component thereby reducing beam diameter ripple. 